1. Field of the Invention
The invention relates to video processing, and in particular to processes which involve motion vector correction for frame rate conversion.
2. Description of the Related Art
Generally, frame rate conversion is used for video standard conversion. For example, a video signal recorded at a frame rate of 24 frames per second (i.e., Hz) may need to be converted to display at a higher display frame rate, such as a 50 Hz television signal under a PAL standard. Moreover, when the 50 Hz television signal under the PAL standard is replayed as a 60 Hz television signal under an NTSC standard, a conversion of the television signals is also required to convert the display frame rate is converted from 50 Hz to 60 Hz.
In this case, frame repetition methods, such as pull-down conversions, are commonly used to perform frame rate up-conversion by repeating frames. However, frame repetition may generate undesirable judder artifacts, when objects or backgrounds of the frames are moving, thus resulting in deterioration of video quality.
To remove the defects of frame rate conversion caused by motion of objects in frames, a technique of motion judder cancellation (MJC) involving motion estimation/motion compensation (ME/MC) has been proposed. Motion judder cancellation generates an intermediate frame by spatially interpolating the position of objects from two or more successive frames according to motion vector information, so as to reduce judder artifacts. Since the motion vector information describes the movements of the objects, most pixels of the intermediate frame along the object motion can be well interpolated along corresponding motion vectors. However, interpolation error may occur around edges of objects in motion, especially during acceleration or retardation. If incorrect edge information derived from motion estimation fails to match the real edges of moving objects, unnatural ringing artifacts or a so-called “halo”, are formed as jagged contours or fuzzy lines in the vicinity of the sharp edges of the moving objects within the intermediate frame.
Thus, it is crucial to perform motion vector correction for frame rate conversion that achieves removal of visible artifacts on the edges of moving objects within an intermediate frame.